Meaning
Atmospheric composition standards define the concentration of contaminants allowed in the gas stream used for sample transport. Nitrogen carrier gas purity describes the level of oxygen and moisture absent from the nitrogen used in moisture analyzers and thermal analysis equipment. For Karl Fischer oven systems, the gas must be dry enough that it does not introduce external moisture into the titration cell.
High purity levels, typically 99.999 percent or better, are required to ensure that the measured water originates solely from the polymer sample.
Contamination Risk
Trace amounts of oxygen in the gas can cause the sample to oxidize during the heating phase in the oven. When nitrogen carrier gas purity is low, the resulting chemical changes can release volatiles that interfere with the detector. This leads to an overestimation of the water content.
Analytical Integrity
System drift is often a direct result of moisture leaking into the gas lines or low quality cylinders. Maintaining high nitrogen carrier gas purity is the first step in calibrating a moisture analyzer for resins like nylon 66. If the carrier gas is wet, the instrument will record a constant background moisture level.
This background makes it difficult to detect the low ppm levels of water required for high quality moulding.
Operational Cost
Procurement of high grade gas cylinders or the installation of inline purifiers represents a necessary expense for a modern lab. While nitrogen carrier gas purity adds to the cost per test, it prevents the far larger costs associated with rejected production lots. Reliable gas supplies ensure that the laboratory data is a true reflection of the resin state.
